PREFACE
Tu1s manual outlines a procedure for developing, evaluating,
 and installing measurement methods in vocational
selection. It explains how to construct vocational tests and
how to determine their reliability and validity. The construction
 and validation of rating scales, interest questionnaires,
 application forms, interview methods, and similar
devices used in determining aptitudes also come within its
scope.
So complex is the task of occupational analysis and individual
 placement, so numerous are the independent variables,
that to some it has seemed futile to expect the ideals of
science and the methods of measurement to be applicable.
Others have gone to an opposite extreme, seeing in the precision
 of test technique a quick relief from the uncertainties
of personal impression. Neither of these views is justified.
Measurement in vocational selection has gradually shown
itself to be a feasible though slowly attainable goal. The
techniques of experiment and statistical method have had,
here as elsewhere, their notable triumphs. But science is
not an easy mistress. She opens no broad highroad to success
 in selecting employees. Only a pseudo-science, ignorant
of statistical requirements and the standards of proof, could
pretend to teach how to read character at sight or claim
100% accuracy in vocational selection.
The search for genuinely scientific means of gaging abilities,
 demonstrably sound in principle and at the same time
practicable, economical, useful in the routine of hiring and
placement, is in itself a rather complicated process. This
process of research, this adaptation of the universal principles
 of inductive logic or scientific method to the particular
task of discovering, developing, and testing new methods of
personnel selection, forms the subject-matter of this manual.

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